The present invention relates to a highly tensioned suspended pipeline and method of installing and in one aspect relates to a highly tensioned suspended pipeline which is especially useful in ice-rich, permafrost regions, rugged terrain, and across active seismic faults.
It is well known that land-based pipelines are commonly used to transport hydrocarbons (e.g. oil and/or gas) from remote production areas to processing and/or end use facilities. Due to esthetics, economics, and other reasons, these pipelines are typically buried in the ground wherever practical. However, in some regions, buried pipelines can not be used because of the nature of the terrain through which the pipeline passes; e.g. ice-rich, permafrost regions, rugged terrain, active seismic faults, etc. In these types of terrain, elevated pipelines are often used to transport the hydrocarbons to their destinations.
For example, in building conventional elevated pipelines across permafrost terrain of North Slope, Alaska, a plurality of substantially aligned, vertical supports (e.g. 5-foot tall) are installed across the terrain at approximately 45 to 65 foot intervals. A long section of pipeline is welded together and then raised onto these vertical supports. Sliding surfaces are provided between the pipeline and each of the vertical supports to thereby allow slight relative movement therebetween. At spaced intervals, (e.g. 1500 feet), the pipeline is fixed to a vertical and horizontal anchor.
xe2x80x9cExpansion loopsxe2x80x9d are spaced (e.g. every 1500 feet) within the pipeline to compensate for any substantial thermal expansion/contraction of the pipeline between any two adjacent fixed anchors. Therefore, every mile of conventional, elevated pipeline normally requires about 100 vertical supports, 100 sliding surfaces, 4 expansion loops, and 4 fixed anchors required thereby producing a relatively large xe2x80x9cfootprintxe2x80x9d (i.e. the actual surface area required in install the pipeline) and numerous ground penetrations for pilings and the like. The xe2x80x9cfootprintxe2x80x9d and the number of ground penetrations may be both esthetically and ecologically undesirable in many regions where such pipelines are needed. Further, the installation of many, closely-spaced vertical supports, anchor supports, and the expansion loops required for a conventional elevated pipeline is both expensive and time-consuming.
Accordingly, it should readily be apparent that there is a continuing need to improve elevated pipelines while, at the same time, reducing the costs of installation. Also, in ecology-sensitive areas such as those covered by tundra/permafrost, it is important to reduce the xe2x80x9cfootprintxe2x80x9d of the pipeline without reducing the reliability/durability of the pipeline.
The present invention provides a highly tensioned, suspended pipeline (HTSP) which is especially useful in permafrost regions, rugged terrain, and across active seismic fault areas and a method for installing the pipeline. Basically, the pipeline is comprised of segments which are fluidly connected together to form the desired length of the line. Each segment is comprised of a length of pipeline which extends between two fixed anchors and which is suspended over a plurality of vertical support towers which are spaced between the two anchors. The length of pipeline is greater than the distance between the anchors to allow the pipeline to sag significantly between adjacent vertical supports.
More specifically, each segment of HTSP is comprised of a first fixed anchor support at the beginning of the segment and a second fixed anchor support at the other end of said segment. A plurality of vertical supports are spaced at intervals between the two anchors. A length of pipeline is anchored at one end to the first anchor and tensioned from the other end as it lays on the ground along side the vertical supports. The pipeline is of sufficient length to permit said pipeline to sag significantly in a downward arc between adjacent vertical supports to a low point which is about 5 feet above the ground when the pipeline is positioned on the vertical supports. Intermediate supports are positioned between adjacent vertical supports to reduce transverse movement of the pipeline.
Preferably, each vertical support is comprised of a base which is affixed to said ground and which has a support frame pivotably mounted thereon. The pipeline is secured in a saddle assembly which, in turn, is pivotably attached to the upper end of the support frame. A flexible sleeve can be positioned on the pipeline at the point where the pipeline is secured within the saddle assembly to prevent crimping and/or flattening during bending of the pipeline.
To install the segment of the present HTSP, the first and second anchors are installed from about 1 mile to about 1.5 miles apart. The vertical supports are positioned at spaced intervals (e.g. 500-700 feet) between said first and said second anchors. The required length of pipeline is assembled and lies on the ground between said first and said anchors with the length of pipeline being greater than the distance between the two anchors. One end of the pipeline is fixed to said first anchor and a tensile force is applied in the pipeline by pulling on the other end.
The length of pipeline is then sequentially lifted onto said vertical supports at predetermined pick-up points while tension is maintained in the pipeline whereby the pipeline becomes supported on the vertical supports. The pick-up points are chosen so that the pipeline will sag significantly in a downward arc between adjacent vertical supports to a low point (e.g. a point about 5 feet off the ground). As the last saddle assembly is lifted onto its respective vertical support, a stop, affixed to the other end of the pipeline, will press against the second anchor and be able to rotate about the horizontal axis that, in turn, is perpendicular to the pipeline and parallel to the ground. Basically identical additional segments of the pipeline are then installed and fluidly connected together to complete the HTSP of the present invention.